Generally, since a secondary battery may be charged and discharged unlike a primary battery, the secondary battery has been applied to various fields such as a digital camera, a cellular phone, a notebook, and a hybrid vehicle and has been actively studied. An example of the secondary battery includes a nickel-cadmium battery, a nickel-metal hydride battery, a nickel-hydrogen battery, and a lithium secondary battery. Among these secondary batteries, the lithium secondary battery having high energy density and discharging voltage has been mainly studied and has been commercialized and widely used.
In addition, the lithium secondary battery may be manufactured in various types. As a typical type of the lithium secondary battery, there are a cylinder type and a prismatic type that may be mainly used for a lithium ion battery. A lithium polymer battery that has been recently spotlighted is manufactured in a pouch type having flexibility, such that a shape thereof is relatively free.
In this case, the pouch type secondary battery is formed to have an electrode body sealed by a pouch so that the electrode body is accommodated in the pouch and electrode tabs connected to the electrode body are protruded to the outside.
However, the pouch type secondary battery described above causes a swelling phenomenon that gas is generated in the pouch at a high temperature by a temperature increase according to the charging and discharging to thereby swell the pouch. Accordingly, an interface resistance of the electrode body is increased, such that performance of the secondary battery may be degraded. In addition, the electrode body is deformed due to the swelling phenomenon to thereby cause a fine short circuit, such that a risk of ignition may be increased.